1. Field of the Invention
The present invention relates to improved polyolefin articles and a method of making such articles. Specifically, the present invention relates to a polyolefin article exhibiting a modified surface and a method of making the article.
2. Description of the Related Art
The use of various polyolefin compositions for forming a variety of shaped articles is known. For example, polyolefins are known to be useful in forming fibers which can be formed into a variety of woven and nonwoven materials. Such polyolefin materials generally possess a relatively hydrophobic (nonwettable) surface. When it is desired to employ a woven or nonwoven material in an absorbent product such as a diaper, bandage, adult incontinent product, training pant, feminine napkin, or the like, it is often desirable that such material exhibit a generally hydrophilic (wettable) surface in order to allow water to pass therethrough.
In the past, when it has been desired to employ a woven or nonwoven polyolefin material in a personal care product, for other than the backing material, it has been suggested to render the polyolefin material wettable (hydrophilic) by applying a surface treatment, such as a surfactant, to the polyolefin. Unfortunately, such surface treatments are generally fugitive in nature. That is, while appearing wettable for an initial application of liquid, after a given amount of water has passed through the polyolefin material, the surface treatment tends to wash off of the polyolefin material. Obviously, after the surface treatment has been washed off the polyolefin material, the polyolefin material is generally no longer capable of exhibiting a wettable (hydrophilic) surface and, instead, exhibits its natural hydrophobic surface.
When polyolefin materials are employed in personal care products, such as diapers, it is likely that they will be required to pass relatively large quantities of liquid waste and will be subjected to multiple insults of liquid waste. When polyolefin fabrics having a surfactant type surface treatment are employed in a diaper, they are generally capable of passing at least the first urine insult but become less capable of passing urine with each subsequent insult. Since a diaper may generally be subjected to three or more urine insults, surfactant treated polyolefin materials have proven generally unsatisfactory for use in certain applications.
Accordingly, attempts have been made to develop a surface treatment for polyolefin materials, which surface treatment is generally not fugitive, thereby rendering said polyolefin fiber wettable on a more permanent basis. For example, U.S. Pat. No. 4,578,414, issued Mar. 25, 1986, to Sawyer et al. is directed to wettable olefin polymer fibers. Described are olefin fibers which are rendered wettable by having incorporated therein at least one wetting agent of the group comprising (a) an alkyoxylated alkyl phenol along with a mixed mono-, di-, and/or tri-glyceride, or (b) a polyoxalkylene fatty acid ester, or (c) a combination of (b) and any part of (a). The invention is said to differ from the prior art by incorporating the surface active agent directly into the bulk polymer resin rather than introducing a copolymer or applying a surface treatment to fabricated fibrous structures.
When the surface active agent is incorporated directly into the bulk polymer resin, the surface active agent must migrate to the surface of the formed article in order to render the surface wettable. Certain disadvantages are associated with such a method. Initially, the blending of the surface active agent into the polymer, through a physical mixing, is a separate process which increases the cost of the final product. Additionally, the choice of surface active agent is limited in that the agent must be able to withstand mixing at elevated temperatures and must exhibit the desired migrating behavior, unless it shear segregates.